Hanlon M R, Begum R R, Newbold R J, Whitford D, Wallace B A
Department of Crystallography, Birkbeck College, University of London, London WC1E 7HX, UK.
Biochem J. 2000 Nov 15;352 Pt 1(Pt 1):117-24.
The cytochrome b(5) tail is a 43-residue membrane-embedded domain that is responsible for anchoring the catalytic domain of cytochrome b(5) to the endoplasmic reticulum membrane. Different models for the structure of the membrane domain of cytochrome b(5) have been proposed, including a helical hairpin and a single transmembrane helix. In the present study, CD spectroscopy was used to investigate the conformation of the tail in different environments, and as a function of temperature, with the goal of understanding the nature of the membrane-bound conformation. Whereas residue property profiling indicates that bending of a helix in the middle of the peptide might be possible, the experimental results in small unilamellar vesicles and lysophosphatidylcholine micelles are more consistent with a single transmembrane helix. Furthermore, although there is evidence for some refolding of the polypeptide with temperature, this is not consistent with a hairpin-to-transmembrane transition. Rather, it appears to represent an increase in helical content in fluid lipid environments, perhaps involving residues at the ends of the transmembrane segment.
细胞色素b(5)的尾部是一个由43个氨基酸残基组成的膜嵌入结构域，负责将细胞色素b(5)的催化结构域锚定在内质网膜上。关于细胞色素b(5)膜结构域的结构，已经提出了不同的模型，包括螺旋发夹模型和单个跨膜螺旋模型。在本研究中，利用圆二色光谱（CD光谱）研究了该尾部在不同环境下以及作为温度函数的构象，目的是了解膜结合构象的本质。虽然残基性质分析表明肽中间的螺旋可能发生弯曲，但在小单层囊泡和溶血磷脂酰胆碱胶束中的实验结果更符合单个跨膜螺旋模型。此外，尽管有证据表明多肽会随温度发生一些重折叠，但这与从发夹结构到跨膜结构的转变不一致。相反，这似乎代表了在流动性脂质环境中螺旋含量的增加，可能涉及跨膜片段末端的残基。
